Looks like the magnetron tube out of a radar set.
I've taken a ship radar set apart once (manufactured in 1973), see this link for a picture of the entire unit:
http://www.anotherpower.com/gallery/dinges/radar_001
Your magnetron came likely out of a similar assembly.
It contains the magnetron tube on the left (with yellow & green wire coming out of it), a klystron tube on the right (KSB9-20), and a 'blocking tube' in the middle (SB-180). At the bottom right is the detector diode (solid state Germanium 
)
Your magnetron could've come out of a similar naval radar set.
I personally get very annoyed when people start applying power to things they have no idea of what it is, thus most likely ruining it, but it's yours so you're free to do with it as you like.
Doubt it's of little use, unless you're a HAM perhaps. The klystrons were used quite a bit for 10 GHz work in the past but have been made obsolete by Gunn diodes; the magnetron (a pulse magnetron most likely, not a continuous one as in your microwave) is pretty useless.
Regards,
